1. Field of the Invention
The present invention relates to a method for manufacturing an optical pickup. The invention in particular relates to a manufacturing method for an optical pickup in which a movable member carrying an objective lens is movably supported by a fixed member through a plurality of elastic support members.
2. Prior Art
An optical pickup is used to read information from (i.e. playback) or write information onto (i.e. recording) an optical recording medium such as a CD (compact disc) or a DVD (digital versatile disc). Such an optical pickup is expected to record/play information reliably without being affected by the wobble of the information recording surface or track of the optical recording medium. For this purpose, the optical pickup needs to have a mechanism of moving an objective lens in a vertical direction (focusing direction) and in a direction orthogonal to the optical axis of the objective lens (tracking direction) while keeping the objective lens horizontal. In this way, it is possible to include a desired position on the information recording surface of the optical recording medium in the focus depth of the objective lens, and to have the laser beam accurately follow the track of the optical recording medium.
One example of this mechanism is explained below. A movable member carrying an objective lens and a fixed member are connected to each other by a total of four elastic support members, that is, two elastic support members arranged in a vertical direction on one side of the objective lens and two elastic support members arranged in the vertical direction on the other side of the objective lens. These elastic support members are connected to the movable member and the fixed member using solder or an adhesive.
When solder is used, however, the influence of heat generated from the molten solder extends to the connecting parts, which tends to cause the movable member or the fixed member to become thermally deformed. Hence it is difficult to ensure the precise connection positions of the elastic support members. When an adhesive is used, on the other hand, the shrinkage of the adhesive as a result of hardening is relatively high, which tends to cause the elastic support members to be displaced.
In view of this, a method of manufacturing an optical pickup by connecting the elastic support members to the movable member and the fixed member by means of insert molding has been proposed (Unexamined Japanese Patent Application Publication No. H10-69655). According to this method, both end portions of each elastic support member are inserted into the movable member and the fixed member when injection-molding the movable member and the fixed member.
FIG. 1 is a perspective view of an optical pickup 400. In this optical pickup 400, four elastic support members 403a, 403b, 403c, and 403d have their end portions inserted in a lens holder (movable member) 402 and a stator (fixed member) 404 by insert molding. FIG. 2 shows manufacturing steps of this insert molding.
In FIG. 2, two suspension sheets 413 which each have two elastic support members 403 are inserted into a mold (not illustrated), along the upper and lower surfaces of a slide core 412a having a depression 402c and a slide core 412b having a depression 402d (step 1). The slide cores 412a and 412b are then slid toward each other along the elastic support members 403, until they come in substantial contact with each other at a predetermined position (step 2). Here, the depression 402c of the slide core 412a faces the depression 402d of the slide core 412b. This being so, a hole 412e is formed when the slide cores 412a and 412b are in contact with each other. Following this, the mold is closed from above and below the slide cores 412a and 412b (in the vertical direction designated by the arrows in step 3 in the drawing), so as to form mold cavities for molding the stator 404 and the lens holder 402 and also to clamp the elastic support members 403 with the slide cores 412a and 412b and the upper and lower halves of the mold (step 3). Then insert molding is performed by pouring a resin into the mold cavities to mold the stator 404 and the lens holder 402 with the elastic support members 403 being partially inserted in the stator 404 and the lens holder 402 (step 4). After this, the mold and the slide cores 412a and 412b are removed (step 5), and the elastic support members 403 are detached from the suspension sheets 413 (step 6).
As a result of this insert molding, the stator 404 and the lens holder 402 are connected to each other by the four elastic support members 403. By mounting an objective lens 401, a focusing coil 405, tracking coils 406, and the like onto this construction, the optical pickup 400 is completed. According to this method, an optical pickup can be manufactured without suffering from the aforementioned problems associated with soldering and adhesion.
This optical pickup 400 is equipped with an MC (moving coil) actuator in which the focusing coil 405 and the tracking coils 406 are mounted on the movable member (lens holder 402). This being so, two elastic support members 403 out of the four elastic support members 403 act as wires for supplying power to the focusing coil 405, and the remaining two elastic support members 403 act as wires for supplying power to the tracking coils 406.
To adapt to the recent demand for high-performance optical pickups, the above type of optical pickup often includes additional electrical/electronic components such as a liquid crystal tilt correction component for making corrections for optical aberration and a numerical aperture changing component for changing an optical constant. To ensure high optical properties, it is desirable for these electrical/electronic components to be mounted on the movable member on which the objective lens is mounted, so as to maintain their relative positions with the objective lens. In such a case, additional wires, i.e., additional elastic support members, for these electrical/electronic components are required.
According to the above manufacturing method, however, it is not practical to add more elastic support members in the focusing direction. It may not be altogether impossible to add one more elastic support member on both sides of the objective lens in the focusing direction by using one more suspension sheet and one more pair of slide cores. However, this requires an extremely complex mold structure, and causes a significant drop in productivity. Hence the above manufacturing method cannot be employed in this case.
On the other hand, it is possible to add elastic support members necessary for wiring on both sides of the existing elastic support members in the horizontal direction (tracking direction). This, however, causes an increase in size of the entire optical pickup.